In the simplest terms, the spine is a column made of vertebrae and discs. The vertebrae provide the support and structure of the spine while the spinal discs, located between the vertebrae, act as cushions or “shock absorbers.” These discs also contribute to the flexibility and motion of the spinal column. FIG. 1A (described in greater detail below) shows a perspective view of a healthy vertebral column including a disc separating vertebrae.
Over time, the discs may become diseased or infected, develop deformities such as tears or cracks, or simply lose structural integrity, for example discs may bulge or flatten. These impaired discs can affect the anatomical functions of the vertebrae, due to the resultant lack of proper biomechanical support, and are often associated with chronic back pain. FIG. 1B (also described in greater detail below) shows a perspective view of a vertebral column including a damaged disc and vertebrae.
Disc degeneration may occur as part of the normal aging process or as a result of traumatic injury to the soft and flexible disc positioned between the vertebrae. The resulting structural collapse under load may cause, among other things, significant pain and loss of motion. Due to these conditions, other health issues may result.
Where the goal of the treatment of such health issues is to rigidly fix individual spinal vertebra after the surgical removal of damaged or diseased disc tissues, the engagement and subsequent integration of implant surfaces in contact with the vertebral bone is required. Rigid fixation helps to enhance immediate recovery from surgery and helps both in the early stages of healing and over the longer term. Loads through daily activities over the longer term are shared between the implanted device, or implant, and the resulting osseous (i.e., comprised of, containing, or resembling bone) growth in and around the device.
Some implants are treated using various methods, including coatings, etching processes utilizing chemicals, and acids resulting in roughened or prepared surfaces that enhance bone in-growth. See, for example, U.S. Pat. Nos. 5,876,453, 5,258,098, 6,923,810 to Michelson and U.S. Pat. No. 7,311,734 to Van Hoeck et al., each of which is incorporated by reference herein. The patterns generated in these processes are often intentionally random and irregular. Many acid-etched surfaces on implant devices, for example, are random and irregular due to the application of masking materials in an intentionally random manner. These surfaces are not optimum because they are inconsistent between devices and are difficult to manufacture with precision and repeatability. Patterned surfaces also typically may have only one depth from the original surface and as a result the depth can have too deep a feature that in effect raises stresses between the bone and implants. By using multiple cuts of a predetermined depth and overlapping at a designed interval the overall effect of improved stability is balanced against over stressing the osseos interface.
Because bone tissues are organic and irregular in their growth patterns, the tissues will adhere in an irregular manner regardless of the surface pattern or orientation. This adherence is often sufficient for the initial stabilization, but not necessarily the most efficient way to prevent movement in the critical early healing phases after implantation. Long-term bone in-growth does not necessarily benefit from the irregular patterns, but is not necessarily hindered by it either.
The stimulation of bone growth through specific patterns include textures and roughness in the macro, micron/submicron and nano sized range also has benefit when coupled to this regular repeating surface architecture. While osseous tissues do not form in regular 3 dimensional structures it does follow a well-established pattern for growth which our device stimulates through the multiple surface preparation steps. The combination of stress induced remodeling of a stimulated bone cell in apposition to this prepared surface results in the overall device enhancing and accelerating the fusion of the device and bone structures. See image of bone structure and the Haversian Canals that typical form in the biologic structure noting the regular patterns at the cellular level e.g., Paul R. Odgren et al.; “Bone Structure” Encyclopedia of Endocrine Disease, Vol. 1, pp. 392-400 (2004) which is incorporated by reference herein.
Optimizing the pattern of the surface, but intentionally removing materials in patterns and through defined depths of features (e.g., teeth, grooves, sharp edges, ridges, anchoring fins (barbs) and shapes (e.g. U.S. Pat. No. 5,207,709, Picha also incorporated by referenced herein), may improve the biological growth of the tissues. Often this result is achieved with very large surface features machined or molded into implant devices. Larger features have an unintentional and difficult-to-measure side effect of localizing forces and can, over time, result in changing osseous integration. Therefore, the device becomes less stable or, through stress, induces necrosis remodeling. This is a commonly observed result in orthodontic treatment where loading is focused to move teeth in a patient's mouth to reposition dentition in a more effective location for mastication and esthetics. Although it is understood that loading can move and reshape bones, each patient and even each area of the skeletal structure is variable and therefore ideal large features often do not work in all applications and all patients. Other factors such as overall health, subsequent health conditions, degenerative conditions, and traumatic events add to this dynamic environment.
Other problems confront surgeons. For example, some surfaces are random and not well suited to the location of implantation, direction of loading, and forces acting on the implants due to daily activities. The results may include poor support of the spinal column or traumatic surgeries. These, in turn, may result in complications and increase patient traumatic suffering. Orientation of the surface patterns in parallel to the original surfaces is also enhanced by the depth of surface cuts and planes that can be designed to function more effectively in resisting directional loading and to be an advantage of a designed surface having three components, namely the width, length and also depth of the designed patterns.
To overcome the shortcomings of conventional spinal implants, a new spinal implant having an improved surface treatment is provided. An object of the present invention is to provide an implant surface having a pattern that is substantially uniform over the area of the implant that is intended to bond to the bone in which the implant is placed. A related object is to provide an improved surgically implantable device having on its surface a substantially uniform and bioactive micromorphology. It is another object of the invention to provide a process or processes for manufacturing such improved implant devices. A more specific object is to provide an improved process that yields a substantially uniform surface topography designed intentionally to enhance healing and long term function of surgically implantable devices.
It is to be understood that the present invention while directed primarily to spinal implants is not limited thereto. The advantageous implant surface created in practice of this invention obtains a surprising and unexpected osteointegration in the context of spinal repair that can be applicable in other situations. It is believed that the present invention can be applied in many medical circumstances where bone in-growth to the surface of a prosthetic device is important to the success of the cosmetic or therapeutic procedure. For example, lower body bone repair, e.g., foot/ankle, and dental prosthetic procedures utilizing prosthetic devices where bone in-growth is required are likely to have their success significantly improved by the use of devices having surfaces produced according to this invention.